Most experienced players agree that there is not enough to distinguish between different artifacts in the game. A few are very useful, the others are rarely worth bothering to lug around. Many people have discussed how to improve them in RGRN and IRC. Here is a summary of some of the ideas posted.
Some past threads in RGRN (via Google Groups)::
Some of these ideas have already been implemented in Nephi's enhanced artifacts patch. They are marked below.
There is also the owned artifacts patch by Topi Linkala. If you wish for an artifact there is a chance that the owner of that artifact arrives with the artifact and starts to fight with you.
Derek Ray's Sporkhack contains various artifact fixes, indicated below.
- Too many of the artifacts are longswords. More diversity would be good.
- Too many of the artifacts are weapons. More diversity would be good. For example, items/tools/armor or even food.
- We need an artifact spear, spears are cool!
Beginning with NetHack 3.6.1, several of these ideas have been implemented:
- Demonbane blocks demon gating while wielded.
- Dragonbane confers reflection while wielded.
- Trollsbane prevents trolls from reviving while wielded.
- Ogresmasher grants 25 constitution while wielded.
- All banes warn you of targeted monsters, like Sting does for orcs. 
- All banes give you +d8 to hit and +d20 to damage, rather than +d5 to hit and double damage. This makes them more useful without having to spend skill slots and enchant weapon scrolls.
- foo-banes have a 1/6 chance of cancelling foo monsters (Slash'Em, copied to UnNetHack)
- Demonbane prevents demons' gating ability, but not the magical power of summon nasties. Implemented in 3.6.1.
- Demonbane is a silver mace which does double damage against demons, provides warning against demons, and, when wielded, prevents demons from summoning in your presence. (Sporkhack)
- wielding Demonbane prevents summoning of demons for monsters and player (UnNetHack)
- Dragonbane grants reflection. Implemented in 3.6.1.
- Dragonbane is an unbreakable silver lance (better for Knights).
- Dragonbane is now a normal spear that provides fire, cold, poison, shock, sleep, acid, and disintegration resistance when wielded. It does double damage against dragons, kills dragons instantly 50% of the time on a successful hit, and provides warning against dragons. (Sporkhack)
- On a critical hit, (a "natural 20"), Giantslayer will kill up to seven giants adjacent to you ("Seven at one blow!").
- Giantslayer as a dwarvish mattock, able to destroy boulders thrown at you.
- Giantslayer is now a sling which provides warning against giants. Giantslayer kills giants on _any_ successful hit with a rock fired from this sling. Rocks fired from Giantslayer do +d8 damage. Giantslayer provides strength 18/** when wielded OR in your alternate weapon slot. (Sporkhack)
- Wielding Giantslayer grants STR 18/** (UnNetHack)
- Ogresmasher gives ogre (18/**) strength -- great for Elven Priests!
- Ogresmasher provides CON 25 when wielded, does double damage against all ogres, kills ogres instantly 50% of the time on a successful hit, and provides warning against ogres. (Sporkhack, the CON 25 has been implemented in 3.6.1.)
- Orcrist does +d4 damage against everything, double damage against orcs, and warns of orcs. (Sporkhack)
- Trollsbane gives hungerless regeneration.
- Trolls killed by Trollsbane will not revive. Especially useful for Barbarian quest.
- Trollsbane does double damage against trolls, kills trolls instantly 50% of the time on a successful hit, and dying trolls do not leave a corpse when Trollsbane is wielded. Trollsbane provides hungerless regeneration when wielded. (Sporkhack)
- Werebane is already useful as a silver sabre
- Werebane could grant unchanging and protection from shapechangers.
- Werebane provides polymorph control when wielded. (Sporkhack)
- Grimtooth is now a (permanantly) poisoned weapon. This makes it somewhat useful in the early game (instead of worthless like it is now), but not so much in the late game, where most of the tougher monsters are poison resistant.
- Grimtooth has +d5 to hit. (Sporkhack)
It is generally agreed that Sting should remain as-is.
- Sting does +d3 damage against everything, double damage against spiders, and warns of spiders. (Sporkhack)
- GreyKnight's patch transfers some of Excalibur's powers to a new artifact Clarent (see below)
- Double damage only against undead/demons/chaotics -- it's overpowered as it is!
- Make the arrows never stop flying until they hit a target or an obstacle, regardless of your Strength.
- Would be nice to have a 5%+ chance of instakilling enemies (arrows piercing the heart of <monster>).
- The Sceptre sets Strength to 25 (L's Patch)
- Snickersnee should do 1d12 extra damage, not 1d8, and get +1d5 to hit. This is because it's harder to get than Excalibur, yet generally less powerful. Since it has none of Excalibur's beneficial side effects (nor any of its drawbacks, granted), it should be a more effective weapon.
- Sunsword has a 1 in 3 chance of blinding opponents.
- Sunsword has a light radius of 3 instead of 2. This gives players more of an incentive to wield it when they don't have a lamp.
- Sunsword insta-kills gremlins. (L's patch)
- Sunsword turns trolls to stone. (L's patch)
- Sunsword is now a silver long sword. (Sporkhack)
- The Tsurugi of Muramasa now does double damage instead of +d8. This puts it in the running for the most powerful weapon in the game, which is where it should be. The fact that it is a two-handed weapon balances it somewhat.
- Invoking the Tsurugi raises its enchantment to +1/0/-1 if blessed/uncursed/cursed (L's patch)
- Vorpal Blade now does +d8 to damage, instead of the ridiculously low +1.
- Replaced by Itlachiayaque (below) in L's patch
- Replaced by Stonecutter (below).
- The Heart of Ahriman confers displacement instead of stealth. (L's patch, included in UnNetHack)
- The Heart of Ahriman gives energy regeneration (L's patch)
New Artifact ideas
Part of Malcolm Ryan's planned Alchemist patch. The philosopher's stone is a grey stone which can absorb the essence of a potion and then be used to make other potions.
L's Itlachiayaque patch replaces the Archeologist's quest artifact, the Orb of Detection, with Itlachiayaque, a shield of reflection that in legend was wielded by the Mesoamerican deity Tezcatlipoca.
- Is a shield of reflection (thus, automatically confers 2 AC and reflection).
- Confers ESP, half spell damage and fire resistance when carried.
- When invoked, it creates a stinking cloud that the player can place unless Itlachiayaque is cursed or the player is not an Archeologist.
GreyKnight's Clarent patch complements Excalibur with Clarent the _other_ sword from Arthurian Legend (the sword in the stone). Clarent is an intelligent lawful short sword which can be dual-wielded with Excalibur. See the link above for a list of other powers.
- +d3 to-hit, +d6 damage.
- Double damage against "earth" and "stone" monsters, including earth elementals, xorns, clay and stone golems, gargoyles, and potentially piercers and rock moles.
- Fast digging: digs through rock at the speed of non-hasted walking, and digs through the floor in one turn.
- Blocks stoning from the hissing attack of cockatrices and chickatrices, though not by any other means.
- When invoked, gives the same effect as a blessed potion of object detection.
- Nephi's patch, which has been included in UnNetHack. http://bilious.alt.org/?208